Multi-ratio transmission

ABSTRACT

A multi step transmission comprising planetary gearsets (P 1 , P 2 , P 3 , P 4 ), shafts and shift elements. The sun gear of gearset (P 1 ) couples shaft ( 4 ) which couples housing (G) via brake ( 04 ). The carrier of gearset (P 1 ) couples shaft ( 3 ), which couples housing (G) via brake ( 03 ), drive shaft ( 1 ) via clutch ( 13 ), and shaft ( 6 ) via clutch ( 36 ). Shaft ( 6 ) couples the ring gear of gearset (P 2 ) and the sun gear of set (P 4 ), and, via clutch ( 68 ), shaft ( 8 ), which couples the sun gear of gearset (P 3 ). Shaft ( 1 ) couples the sun gear of gearset (P 2 ) and the carrier of set (P 3 ). Shaft ( 7 ) couples the ring gear of set (P 1 ) and the carrier of gearset (P 2 ). The ring gear of set (P 4 ) couples shaft ( 5 ) which couples housing (G) via brake ( 05 ). Output shaft ( 2 ) couples the ring gear and carrier of gearsets (P 3 , P 4 ) respectively.

This application is a National Stage completion of PCT/EP2010/062128filed Aug. 19, 2010, which claims priority from German patentapplication serial no. 10 2009 028 708.6 filed Aug. 20, 2009.

FIELD OF THE INVENTION

The present invention relates to a multi step transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from theapplicant's patent DE 199 49 507 A1, according to which twonon-shiftable front-mounted gear sets are provided on the drive shaftand generate two rotational speeds on the output side, which, inaddition to the rotational speed of the drive shaft, can be selectivelymeshed with a shiftable double planetary gear set acting on the outputshaft by selective engagement of the shift elements such that only oneof the two currently actuated shift elements must be engaged ordisengaged to shift from one gear to the next higher or lower gear.

By using five shift elements, seven forward gears are obtained; by usingsix shift elements, nine or ten forward gears are obtained.

Furthermore, DE 102 13 820 A1 makes known a multi-speed automatictransmission with eight forward gears and one reverse gear, whichcomprises a first input path T1 of a first transmission ratio; an inputpath T2 that has a higher transmission ratio than that of input path T1;a Ravigneaux type planetary gear set with four elements, namely, a firstelement, a second element, a third element and a fourth element in thesequence of elements in a rotational speed diagram; a clutch C-2 whichtransfers rotation of the input path T2 to the first element S3; aclutch C-1, which transfers rotation from the input path T2 to thefourth element S2; a clutch C-4, which transfers rotation from the inputpath T1 to the first element; a clutch C-3, which transfers rotationfrom the input path T1 to the second element C3; a brake B-1, whichproduces meshing of the fourth element; a brake B-2, which producesmeshing of the second element; and an output element that is coupled tothe third element S3.

Furthermore, a nine-speed multi step transmission is known from DE 29 36969 A1; it comprises eight shift elements and four gear sets, whereinone gear set serves as a front-mounted gear set and the main gearingincludes a Simpson set and a further gear set serving as reversegearing.

Further multi step transmissions are known, for example, from theapplicant's DE 102005010210 A1 and DE 102006006637 A1.

Automatically shiftable vehicle transmissions, of a planetary design,are already generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a low number of shift elements, and minimize the need fordouble shifting when sequential shifting is performed, thereby ensuringthat only one shift element is ever switched when shifting is performedin defined groups of gears.

The applicant's document, DE 102008000428.3 which is not yet published,discloses a multi step transmission of a planetary design that includesan input shaft and an output shaft which are disposed in a housing. Theknown transmission includes at least four planetary gear sets which aredesignated, in the following, as the first, second, third, and fourthplanetary gear sets, at least eight rotatable shafts which aredesignated in the following as the drive shaft, output shaft, third,fourth, fifth, sixth, seventh, and eighth shafts, and at least six shiftelements comprising brakes and clutches, whose selected engagementproduces different transmission ratios between the input shaft and theoutput shaft, such that preferably nine forward gears and one reversegear can be realized.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, form a shiftable front-mounted gear set,wherein the third and fourth planetary gear sets form a main gear set.

In the known multi step transmission, the carriers of the first andsecond planetary gear sets are coupled together via the fourth shaftwhich is connected to an element of the main gear set, the ring gear ofthe first planetary gear set is coupled to the sun gear of the secondplanetary gear set via the eighth shaft, which is detachably connectableto the drive shaft via a first clutch, and the sun gear of the firstplanetary gear set can be coupled to a housing of the transmission bymeans of the third shaft, via a first brake, and is detachablyconnectable to the drive shaft via a second clutch, wherein the ringgear of the second planetary gear set can be coupled to a housing of thetransmission by means of the fifth shaft via a second brake. Inaddition, the seventh shaft is constantly connected to at least oneelement of the main gear set, and can be coupled to a housing of thetransmission via a third brake, wherein the sixth shaft is constantlyconnected to at least one further element of the main gear set and isdetachably connectable to the drive shaft, via a third clutch; theoutput shaft is constantly connected at least to one further element ofthe main gear set.

In the known transmission, the fourth shaft is preferably constantlyconnected to the ring gear of the third planetary gear set, wherein thesixth shaft is constantly connected to the ring gear of the fourthplanetary gear set and to the carrier of the third planetary gear set,and is detachably connectable to the drive shaft via the third clutch.Furthermore, the seventh shaft is constantly connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to ahousing of the transmission via the third brake. In this case, theoutput drive is produced via the output shaft that is constantlyconnected to the carrier of the fourth planetary gear set. Furthermore,the third and fourth planetary gear sets can be combined or reduced to aRavigneaux set having a common carrier and a common ring gear.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a multi steptransmission of the initially described type, which has nine forwardgears and at least one reverse gear having a sufficient transmissionratio, in which the design complexity and the overall size, inparticular the overall length and the weight, are optimized, and inwhich efficiency is improved with respect to drag losses and gearinglosses. In addition, in the multi step transmission according to theinvention, minimal support moments should act on the shift elements. Thetransmission, according to the invention, should be particularly suitedfor a front transverse installation.

Accordingly, a multi step transmission, according to the invention, of aplanetary design is proposed which has an input shaft and an outputshaft which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and at least six shift elements comprising brakes andclutches, whose selective engagement produces different transmissionratios between the drive shaft and the output shaft, such thatpreferably nine forward gears and one reverse gear can be realized.

The planetary gear sets, viewed axially, are disposed in the sequence offirst planetary gear set, second planetary gear set, third planetarygear set, fourth planetary gear set, and are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is fixed, the ring gear hasa direction of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablysupported, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, wherein each inner planetgear meshes with only one outer planet gear. As a result, when thecarrier is fixed, the ring gear has the same direction of rotation asthe sun gear.

According to a preferred embodiment of the invention, the sun gear ofthe first planetary gear set is connected to the fourth shaft which canbe coupled to a housing of the transmission via a first brake, thecarrier of the first planetary gear set is connected to the third shaftwhich can be coupled to a housing of the transmission via a secondbrake, and is detachably connectable to the drive shaft, via a firstclutch, and to the sixth shaft via a second clutch, the sixth shaft isconnected to the ring gear of the second planetary gear set, and to thesun gear of the fourth planetary gear set, and is detachablyconnectable, via a third clutch, to the eighth shaft, which is connectedto the sun gear of the third planetary gear set, and the drive shaft isconnected to the sun gear of the second planetary gear set, and to thecarrier of the third planetary gear set.

Furthermore, the ring gear of the first planetary gear set is connectedto the seventh shaft which is connected to the carrier of the secondplanetary gear set, the ring gear of the fourth planetary gear set canbe coupled to a housing of the transmission via a third brake, and theoutput shaft is connected directly to the ring gear of the thirdplanetary gear set and to the carrier of the fourth planetary gear set.

The embodiment of the multi step transmission, according to theinvention, results in transmission ratios that are particularly suitablefor passenger vehicles, and in a greater overall gear ratio of the multistep transmission, thereby improving driving smoothness andsignificantly reducing fuel consumption.

Furthermore, design complexity is significantly reduced with the multistep transmission, according to the invention, due to a low number ofshift elements. Using the multi step transmission according to theinvention, it is advantageously possible to perform a start-up using ahydrodynamic converter, an external start-up clutch, or any othersuitable external start-up element. It is also conceivable to perform astart-up using a start-up element integrated in the transmission.Preferably, a shift element that is actuated in the first forward gearand in the reverse gear is suitable.

Moreover, the multi step transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Furthermore, low moments are present in the shift elements and in theplanetary gear sets of the multi step transmission, therebyadvantageously reducing wear in the multi step transmission. Inaddition, the low moments make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following, as anexample, with reference to the attached figures. They show:

FIG. 1: a schematic view of a first preferred embodiment of a multi steptransmission according to the invention; and

FIG. 2: an example of a shift pattern for a multi step transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi step transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4 which are disposed in a housing G. Planetary gearsets P1, P2, P3 and P4, in the example shown in FIG. 1, are designed asminus planetary gear sets. According to the invention, at least oneplanetary gear set can be implemented as a plus planetary gear set ifthe carrier and ring gear connection are exchanged and, simultaneously,the value of the stationary transmission ratio is increased by 1 incomparison to the embodiment as a minus planetary gear set.

In the embodiment shown, the planetary gear sets, viewed axially, aredisposed in the sequence P1, P2, P3 and P4.

As shown in FIG. 1, six shift elements are provided, namely, threebrakes, 03, 04, 05 and three clutches 13, 36, and 68. The spatialdisposition of the shift elements can be arbitrary, and is limited onlyby the dimensions of the outer design. The clutches and the brakes ofthe transmission are preferably implemented as friction shift elementsor lamellar shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi step transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft isthe first shaft, and the output shaft is the second shaft of thetransmission.

According to the invention, in the multi step transmission according toFIG. 1 it is provided that the sun gear of the first planetary gear setP1 is connected to the fourth shaft 4 which can be coupled to a housingG of the transmission via a first brake 04, the carrier of the firstplanetary gear set P1 is connected to the third shaft 3 which can becoupled to a housing G of the transmission via a second brake 03, and isdetachably connectable to the drive shaft 1 via a first clutch 13, andto the sixth shaft 6 via a second clutch 36.

As shown in FIG. 1, the sixth shaft 6 is connected to the ring gear ofthe second planetary gear set P2, and to the sun gear of the fourthplanetary gear set P4, and is detachably connectable via a third clutch68 to the eighth shaft, which is connected to the sun gear of the thirdplanetary gear set P3, and the drive shaft 1 is connected to the sungear of the second planetary gear set P2, and to the carrier of thethird planetary gear set P3.

According to the invention, the ring gear of the first planetary gearset P1 is connected to the seventh shaft 7 which is connected to thecarrier of the second planetary gear set P2, the ring gear of the fourthplanetary gear set P4 is connected to the fifth shaft 5 which can becoupled to a housing G of the transmission via a third brake 05; in theembodiment shown, the output shaft 2 is connected directly to the ringgear of the third planetary gear set P3 and to the carrier of the fourthplanetary gear set P4.

According to the invention, the first clutch 13, viewed axially, can bedisposed between first and the second planetary gear sets P1, P2,wherein the third clutch 68, viewed axially, can be disposed between thesecond and third planetary gear sets P2, P3.

Furthermore, the second and first brakes 03, 04 and the second clutch36, viewed axially, are preferably disposed next to each other.

FIG. 2 shows an example of a shift pattern of a multi step transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps, and, to be determined therefrom, thegear increments or step changes phi to the next higher gear, wherein thevalue 9.003 is the transmission ratio spread.

Typical values for the stationary transmission ratios of the planetarygear sets P1, P2, P3 and P4 implemented as minus planetary gear sets are−3.90, −1.60, −2.201 and −2.103, respectively. FIG. 2 shows that doubleshifting or group shifting is avoided when shifting sequentially sincetwo adjacent gear steps share two shift elements. It is also shown thata large transmission ratio spread is attained with small gearincrements.

The first forward gear it attained by engaging the first and thirdbrakes 04, 05 and the second clutch 36; the second forward gear isattained by engaging the third brake 05 and the first and secondclutches 13, 36; the third forward gear is attained by engaging thefirst and third brakes 04, 05 and the first clutch 13; the fourthforward gear is attained by engaging the third brake 05 and the firstand third clutches 13, 68; the fifth forward gear is attained byengaging the first brake 04 and the first and third clutches 13, 68; thesixth forward gear, which is preferably implemented as direct drive, isattained by engaging all of the clutches 13, 36, 68; the seventh forwardgear is attained by engaging the first brake 04 and the second and thirdclutches 36, 68; the eighth forward gear is attained by engaging thesecond brake 03 and the second and third clutches 36, 68; and the ninthforward gear is attained by engaging the first and second brakes 04, 03and the third clutch 68, and the reverse gear is attained by engagingall of the brakes 03, 04, and 05.

Since the brakes 04 and 05 are engaged in the first forward gear and inthe first reverse gear, these shift elements can be used as start-upelements.

According to the invention, different gear increments can also resultfrom the same gear pattern depending on the shift logic, thereby makingit possible to realize an application-specific or vehicle-specificvariation.

According to the invention, it is possible to provide additionalfreewheels at each suitable location of the multi stepped transmission,for example, between a shaft and the housing, or possibly to connect twoshafts.

According to the invention, an axle differential and/or a distributordifferential can be disposed on the drive side or on the output side.

Within the scope of an advantageous development, the drive shaft 1 canbe separated from a drive motor, as needed, by a clutch element, whereina hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, awet start-up clutch, a magnetic powder clutch, or a centrifugal clutchcan be used as the clutch element. It is also possible to dispose such astart-up element in the power flow direction after the transmissionwherein, in this case, the drive shaft 1 is continuously connected tothe crankshaft of the engine.

The multi step transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the engine andthe transmission.

Within the scope of a further, not represented embodiment of theinvention, a wear-free brake, for instance, a hydraulic or electricretarder or the like, can be disposed on each shaft, preferably on thedrive shaft 1 or the output shaft 2, which is of special significancefor use in commercial vehicles in particular. Furthermore, a powertake-off drive can be provided on each shaft, preferably on the driveshaft 1 or the output shaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi step transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

Obviously, any structural embodiment, in particular any spatialdisposition of the planetary gear sets and the shift elementsindividually and relative to each other, and insofar as it istechnically expedient, falls under the scope of protection of thepresent claims, without influencing the function of the transmission asspecified in the claims, even if these embodiments are not explicitlyrepresented in the figures or in the description.

REFERENCE CHARACTERS

-   1 First shaft, drive shaft-   2 Second shaft, output shaft-   3 Third shaft-   4 Fourth shaft-   5 Fifth shaft-   6 Sixth shaft-   7 Seventh shaft-   8 Eighth shaft-   03 Second brake-   04 First brake-   05 Third brake-   13 First clutch-   36 Second clutch-   68 Third clutch-   P1 First planetary gear set-   P2 Second planetary gear set-   P3 Third planetary gear set-   P4 Fourth planetary gear set-   i Transmission ratio-   phi Step change-   G Housing

The invention claimed is:
 1. A multi step transmission of a planetarydesign for an automatic transmission for a motor vehicle, the multi steptransmission comprising; a drive shaft (1); an output shaft (2); first,second, third and fourth planetary gear sets (P1, P2, P3, P4) which aredisposed in a housing (G), each of the first, the second, the third, andthe fourth planetary gear sets (P1, P2, P3, P4) comprising a sun gear, acarrier and a ring gear; a third rotatable shaft (3), a fourth rotatableshaft (4), a fifth rotatable shaft (5), a sixth rotatable shaft (6), aseventh rotatable shaft (7), and an eighth rotatable shaft (8); at leastsix shift elements (03, 04, 05, 13, 36, 68) comprising a first brake(04), a second brake (03), a third brake (05), a first clutch (13), asecond clutch (36) and a third clutch (68) whose selected engagementproduces different transmission ratios between the drive shaft (1) andthe output shaft (2) such that nine forward gears and one reverse gearcan be achieved; wherein the sun gear of the first planetary gear set(P1) is connected to the fourth shaft (4) which is connectable to thehousing (G) of the transmission via the first brake (04); the carrier ofthe first planetary gear set (P1) is connected to the third shaft (3)which is connectable to the housing (G) of the transmission, via thesecond brake (03), and is connectable to the drive shaft (1), via thefirst clutch (13), and to the sixth shaft (6), via the second clutch(36); the sixth shaft (6) is connected to the ring gear of the secondplanetary gear set (P2) and the sun gear of the fourth planetary gearset (P4), and is connectable, via the third clutch (68), to the eighthshaft (8) which is connected to the sun gear of the third planetary gearset (P3); the drive shaft (1) is connected to the sun gear of the secondplanetary gear set (P2) and the carrier of the third planetary gear set(P3); the seventh shaft (7) is connected to the ring gear of the firstplanetary gear set (P1) and the carrier of the second planetary gear set(P2); the ring gear of the fourth planetary gear set (P4) is connectedto the fifth shaft (5) which is connectable to the housing (G) of thetransmission via the third brake (05); and the output shaft (2) isconnected to the ring gear of the third planetary gear set (P3) and thecarrier of the fourth planetary gear set (P4).
 2. The multi steptransmission according to claim 1, wherein the first, the second, thethird and the fourth planetary gear sets (P1, P2, P3, P4) are minusplanetary gear sets.
 3. The multi step transmission according to claim1, wherein a first forward gear is attained by engagement of the firstand the third brakes (04, 05) and the second clutch (36); a secondforward gear is attained by engagement of the third brake (05) and thefirst and the second clutches (13, 36); a third forward gear is attainedby engagement of the first and the third brakes (04, 05) and the firstclutch (13); a fourth forward gear is attained by engagement of thethird brake (05) and the first and the third clutches (13, 68); a fifthforward gear is attained by engagement of the first brake (04) and thefirst and the third clutches (13, 68); a sixth forward gear is attainedby engagement of the first, the second and the third clutches (13, 36,68); a seventh forward gear is attained by engagement of the first brake(04) and the second and the third clutches (36, 68); an eighth forwardgear is attained by engagement of the second brake (03) and the secondand the third clutches (36, 68); a ninth forward gear is attained byengagement of the first and the second brakes (04, 03) and the thirdclutch (68); and the reverse gear is attained by engagement of thefirst, the second and the third brakes (04, 03, 05).
 4. The multi steptransmission according to claim 2, wherein a first forward gear isattained by engagement of the first and the third brakes (04, 05) andthe second clutch (36); a second forward gear is attained by engagementof the third brake (05) and the first and the second clutches (13, 36);a third forward gear is attained by engagement of the first and thethird brakes (04, 05) and the first clutch (13); a fourth forward gearis attained by engagement of the third brake (05) and the first and thethird clutches (13, 68); a fifth forward gear is attained by engagementof the first brake (04) and the first and the third clutches (13, 68); asixth forward gear is attained by engagement of the first, the secondand the third clutches (13, 36, 68); a seventh forward gear is attainedby engagement of the first brake (04) and the second and the thirdclutches (36, 68); an eighth forward gear is attained by engagement ofthe second brake (03) and the second and the third clutches (36, 68); aninth forward gear is attained by engagement of the first and the secondbrakes (04, 03) and the third clutch (68); and the reverse gear isattained by engagement of the first, the second and the third brakes(04, 03, 05).